While it’s not clear what causes migraines, one of their lasting effects may be brain lesions triggered by poor blood flow.

Researchers report in the Journal of the American Medical Association (JAMA) that women, who are three times as likely as men to experience migraines, may suffer from other consequences of the painful headaches apart from the common symptoms of nausea, vomiting and sensitivity to light. Women who have migraines are twice as likely as non-sufferers to show structural changes, or lesions, due to inadequate blood flow in certain parts of the brain.

The role that these lesions may play in health, however, still aren’t obvious. “Patients should not live with the idea that each migraine attack is potentially ‘damaging’ their brains,” corresponding study author Mark Kruit says in an email to TIME discussing the results. “Patients should know that the [volume] of changes is small, and that they are not related to worse cognitive function. [T]here is no need for changes in the way migraine patients are treated, based on the study results.”

Previous MRI brain scans of migraine patients found unusual “hyperintensities” — bright areas suggesting areas of poor blood flow. But those studies could not determine which came first — whether people with migraines tend to develop brain lesions, or whether the brain lesions trigger migraines. Those studies also could not track whether each successive migraine would expand the size of the brain lesions, leading to worsening symptoms.

So Kruit, a radiologist and neurologist working in Leiden in the Netherlands, joined with a Dutch team of doctors to study migraine in nearly 300 adults living in that country. Most of the participants suffered from migraines, but some did not. Researchers scanned the brains of all of the participants at the start of the study, in 2000, and again in 2009. By comparing the images taken in the same year, Kruit and his colleagues could measure differences in brain lesions between the migraine patients and those who did not suffer from the headaches. And by comparing scans for the same patients taken nine years apart, they could also record whether those with migraine history are more likely to develop new brain lesions over time, whether existing lesions grow faster among people with more migraine attacks, or whether the lesions are linked to declines in cognitive skills.

The researchers found no difference in outcomes among men. Both men with migraines and those without the headaches were equally likely to show hyperintensities on the MRI scans.

But it was a different story for the women. Both in 2000 and in 2009, women with migraines had higher lesion volume than those without migraines, and during the study period their lesions also progressed faster than those among women without migraines. However, the growth of these lesions was not associated with the frequency or intensity of migraines, or to the presence of aura — the vision disturbances and other sensory changes that may precede migraine headaches. That, say the researchers, suggests that the lesions are not part of the collateral damage resulting from the migraine attacks but rather related to whatever is responsible for the headaches.

The lesions that were especially common among women with migraine are called deep white matter hyperintensities. These have been linked in the past to dementia and stroke, but when the Dutch researchers conducted cognitive tests on the migraine participants, they did not observe any declines in cognitive ability or increased stroke risk among headache sufferers in their study relative to those without migraine.

So while women who experience migraines are more likely than other women to develop unusual structural changes in the brain, those changes don’t appear to have any clinical effect.

In fact, as Dr. Deborah Friedman, a neurologist at University of Texas Southwester Medical Center and Dr. David Dodick, in the department of neurology at Mayo Clinic, write in an editorial accompanying the study, the results may actually be “reassuring for patients and their physicians on several levels” since “the overall lesion burden was quite small and most likely clinically insignificant.”

Still, the link between migraines and brain lesions warrants more study, since they appear to be connected to the root cause of the headaches and may help scientists to understand the biology behind them. And that may ultimately lead to better treatments as well.